THE PATHWAYS OF LIGHT MEASURED IN FUNDUS REFLECTOMETRY

We measured the spectral reflectance of the fovea of ten normal subjec ts in four conditions, i.e. under dark-adapted and bleached conditions and at two retinal angles of incidence. The objective was to study op tical pathways through the photoreceptor layer, resulting in a model t hat simultaneously explains spectral, directional and bleaching proper ties of the fovea. On theoretical grounds, we propose that small refle ctions from the stack of discs in the cone outer segments are the orig in of the directional component of foveal reflection. Non-directional reflection occurs at the inner limiting membrane and at all layers pos terior to the outer segments. With four reflectance spectra as input, the model allows determination of the density of the photostable absor bers, the lens, macular pigment, melanin and blood. Because of the sim plified modeling of the layers posterior to the photoreceptor layer, t he values for the density of melanin and blood are not necessarily com parable to physiological data. The density of the visual pigment calcu lated with this model is consistent with psychophysical data, with est imates for the ten subjects ranging from 0.41 to 0.80. The long wavele ngth sensitive cone fraction is calculated as 0.56. Copyright (C) 1996 Elsevier Science Ltd.